Okay at least I was able to access my encrypted drive by using
cryptsetup luksOpen /dev/mydevice mount_point;
installing lvm2 to mount logical volumes;
activating the logical volumes in group qubes_dom0 with vgchange -ay;
listing the volumes with lvs or lvdisplay and mounting the desired vulumes with the mount command;
Now could someone tell me where I can edit Qube Settings > Devices ?
Edit: I don’t need help anymore. It was quicker to reinstall than to wait for a response.